Design of low phase noise InGaP/GaAs HBT-based differential Colpitts VCOs for interference cancellation system

Abstract

This paper presents design, fabrication and characterization of two differential Colpitts voltage controlled oscillator (VCOs) - cross-coupled VCO (CC-VCO) and double cross-coupled VCO (DC-VCO) - in InGaP/GaAs HBT technology. Their main parameters like the oscillation frequency, output power and phase noise performance are measured and compared with other recently published studies. In the cores of two VCOs, two switching transistors are introduced to steer the core bias current to save power. An LC tank with higher inductor quality factor (<i>Q</i>) is used to generate oscillation frequency. The differential CC-VCO exhibited a superior phase noise characteristics of-130.12 dBc/Hz at 1 MHz from the carrier frequency (1.566 GHz) when supplied with a control voltage of 0 volt. In the same way, the differential DC-VCO achieved -134.58 dBc/Hz at 1 MHz from the carrier frequency (1.630 GHz) with the same control voltage. Two pairs of on-chip base collector (BC) diodes are used in the tank circuit to increase the VCO tuning range. It is concluded that the faster switching action of InGaP/GaAs HBT transistors exhibited the excellent phase noise characteristics.